A vitrectomy is surgery to remove some or all of the vitreous gel from the middle of the eye. It may be performed when there is a retinal detachment, because removing the vitreous gel gives better access to the back of the eye. The vitreous gel may also be removed if blood in the vitreous gel does not clear on its own.
After removing the vitreous gel, the surgeon may treat the retina with a laser (photocoagulation), cut or remove fibrous or scar tissue from the retina, flatten areas where the retina has become detached, or repair tears or holes in the retina or macula.
Vitreoretinal surgery is performed in a pressure controlled closed chamber where the infusion of either a balanced salt solution (BSS) or air is pressure regulated. The Alcon™ Constellation™ Vision System is one popular device for carrying our vitreoretinal surgery.
It is necessary to operate in a pressure controlled closed chamber to avoid globe collapse because the eye softens during the fluid aspiration that occurs with vitrectomy and scleral rigidity is required to move the eye and to allow easy instrument exchange. Initially, pressure was provided using gravity to move the BSS from the bottle through the infusion tubing into the eye. The Constellation™ Vision System provides integrated pressurized infusion pressurising BSS fluid in a disposable cassette, measuring the flow into the eye and integrating through the microprocessor of an integrated computer.
The infusion tubing of the Constellation™ Vision System includes an air infusion line which is linked to the BSS fluid infusion line but is protected by a duckbill valve to prevent fluid reflux into the airline to protect the delicate gas pressure controlling mechanism. In two important situations, the current infusion tubing design creates problems, one of which is unregulated and inconsistent pressure whilst the other is potentially very dangerous.
In the first and most common situation, for many procedures a long acting gas mixture is exchanged for the intraoperative gas by performing an “exchange transfusion” where the desired post-operative mixture is flushed through vitreous cavity progressively increasing the concentration from 0% to the desired final concentration (for example 30% SF 6). With the current infusion tubing, the intraocular pressure cannot be regulated during this step and many people allow gas to escape intermittently from an open sclerotomy or vent via a 30 gauge needle inserted via the pars plana relying on the resistance in the fine needle to regulate the pressure. This is problematic because this is venting to atmospheric pressure (0 mmHg) and not to the desired intraocular pressure of around 20 mmHg.
In the second situation, silicon oil is injected at very high pressure that can cause the eye to rupture because there is no feedback system regulating the intraocular pressure during the injection. This has caused rupture of the globe either through the sclera or, for example, corneal graft but can also cause other problems due to the high pressure and shutdown of the retinal circulation.
Indeed, duckbill valves of the current infusion tubing have been associated with infusion bubbles and uncontrolled reflux, which has prompted the repurposing of the duckbill valve with a one-way valve (“Elimination of Infusion bubbles and uncontrolled reflux in the Alcon constellation vitrectomy vision system” Russell, S. R., Sohn, E. H., Boldt, H. C., Folk, J. J., Tarantola, R. M., Kay, C. N., Mahajan, V. B., Retina: 2013; 33(4); 803-6).
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.